The present invention generally relates to surface mount (SM) integrated circuit (IC) devices. More particularly, this invention relates to thermal management of circuit assemblies containing one or more SM IC packages.
IC devices generate heat during their operation, resulting in increased junction temperatures for the devices. Because IC reliability and function are adversely affected by high junction temperatures, various techniques for removing heat from IC devices have been proposed. One approach entails the use of a thermally-conductive substrate or a substrate structurally modified to promote its heat conduction capability. For example, heat-generating semiconductor devices, such as power flip chips and SM packages, are often mounted to alumina substrates that conduct and dissipate heat in the vertical direction beneath the device.
Another approach used with SM IC packages is represented in FIG. 1, and involves an IC package 114 containing a metal slug 116 that conducts thermal energy from the package 114 to a substrate 112 beneath the package 114. Heat can then be removed from the substrate 112 by conduction into a separate heat sink 118 (such as the product case) contacting the backside of the substrate 112 opposite the package 114. As is conventional, FIG. 1 shows the input/output (I/O) pads 122 of the device 120 on the surface of the device 120 opposite the PCB substrate 112 and wire bonded to signal lines (not shown) on the substrate 112. The metal (e.g., copper) slug 116 is soldered to the side of the device 120 facing the PCB substrate 112 (i.e., opposite the I/O pads 122). In the case where the substrate 112 is a printed circuit board (PCB) with limited thermal conductivity, heat removal from the IC device 120 must often be promoted through the use of through-hole vias 124, which are shown as thermally contacting the heat sink 118 through a thermally conductive compound 126.
More recently, commonly-assigned U.S. Pat. Nos. 6,180,436, 6,262,489, and 6,873,043 and U.S. Patent Application Publication Nos. 2005/0040518 and 2005/0078456 teach thermal management techniques compatible with flip chips on PCB's by making use of heat sinks with pedestals that contact the back side of the flip chip, i.e., the surface of the chip opposite the surface on which its microcircuitry is formed. As evident from FIG. 1, such an approach cannot be used with SM packages because of the presence of the I/O pads 122 and bond wires on the side of the package opposite the substrate 112.